Le Forum, Vol. 45 #4

https://digitalcommons.library.umaine.edu/francoamericain_forum/1109/thumbnail.jp

Synthèse d'oxydes de phosphines secondaires chiraux (précurseurs d'organophosphorés chiraux et application en catalyse asymétrique)

La synthèse asymétrique d'Oxydes de Phosphines Secondaires (OPS) a été réalisée à partir d'hydrogénoarylphosphinates de menthyle diastéréomériquement purs par une réaction de substitution nucléophile du groupe ( )-menthyloxy par divers organolithiens. Ces nouveaux OPS, optiquement purs, ont été utilisé en tant qu'intermédiaires pour la synthèse de composés phosphores P-stéréogéniques. Une méthode générale d'accès aux acides phosphineux borane énantiopurs a été développée et les acides phosphineux boranes encombrés ont été convertis en phosphines tertiaires boranes avec un bon contrôle de la stéréochimie. Une application à la synthèse de phosphapalladacycles P-stéréogéniques chiraux a été effectuée à partir d'o-tolylphosphines borane énantiopures. Une réaction asymétrique de cycloaddition [2+1] entre des dérivés bicycliques pontés [2.2.1] et des acétyléniques terminaux catalysée par de complexes associant le palladium II et les OPS énantioenrichis, comme préligands, a été mise au point. Les excès énantiomériques des alkylidène cyclopropanes obtenus atteignent 95%.AIX-MARSEILLE3-BU Sc.St Jérô (130552102) / SudocSudocFranceF

Benchmarking Higher Energy Collision Dissociation (HCD) by Investigation of Binding Energies of Gas-phase Host\textendash Guest Complexes of Hemicryptophane Cages

International audienceSynthesis of host molecules that feature well-defined characteristics for molecular recognition of guest molecules is often a major aim of synthetic host–guest (H–G) chemistry. A key consideration in evaluating the selectivity of hosts and the affinities of guests is the measurement of binding energies of obtained H–G complexes. In contrast to nuclear magnetic resonance (NMR) or fluorescence measurements that are capable of measuring binding strengths in solution, mass spectrometry offers the opportunity to measure gas-phase binding energies. Presented in this article is a higher energy collision dissociation (HCD) approach for determining critical energies of dissociation of H–G complexes. Experiments were performed on electrospray ionization (ESI)-generated H–G pairs in an LTQ-XL/Orbitrap hybrid instrument. The presented HCD approach requires preliminary calibration of the internal energy distribution of generated ions that was achieved by the use of activation parameters that were known from previous low-energy collision-induced dissociation (low-energy CID) experiments. Internal energy deposition was modeled based on a truncated Maxwell–Boltzmann distribution and characteristic temperature (Tchar). Using this method, critical energies of dissociation were determined for 10 H–G biologically relevant complexes of the heteroditopic hemicryptophane cage host (Host). Obtained results are compared with those found previously by low-energy CID. The use of this HCD technique is relatively straightforward, although its implementation does require knowledge (or a presumption) about the Arrhenius pre-exponential factor of the complexes to obtain their critical energies of dissociation

Investigation of hemicryptophane host-guest binding energies using high-pressure collision induced dissociation in combination with RRKM modeling

International audienceIn advancing host-guest (H-G) chemistry, considerable effort has been spent to synthesize host molecules with specific and well-defined molecular recognition characteristics including selectivity and adjustable affinity. An important step in the process is the characterization of binding strengths of the H-G complexes that is typically performed in solution using NMR or fluorescence. Here, we present a mass spectrometry-based multimodal approach to obtain critical energies of dissociation for two hemicryptophane cages with three biologically-relevant guest molecules. A combination of blackbody infrared radiative dissociation (BIRD) and high-pressure collision induced dissociation (high-pressure CID), along with RRKM modeling, were employed for this purpose. For the two tested hemicryptophane hosts, the cage containing naphthyl linkages exhibited stronger interactions than the cage bearing phenyl linkages. For both cages, the order of guest stability is: choline > acetylcholine > betaine. The information obtained by these types of mass spectrometric studies can provide new insight into the structural features that most influence the stability of H-G pairs, thereby providing guidance for future syntheses

Exploring Phosphine Electronic Effects on Molybdenum Complexes: A Combined Photoelectron Spectroscopy and Energy Decomposition Analysis Study

International audienceIn organometallic chemistry, and especially in the catalysis area, accessing the finest tuning of a catalytic reaction pathway requires a detailed knowledge of the steric and electronic influence of the ligands bound to the metal center. Usually, the M-L bond between a ligand and a metal is depicted by the Dewar-Chatt-Duncanson model involving two opposite interactions, a σ-donor and a π-acceptor effect of the ligand. The experimental evaluation of these effects is essential and complementary to in-depth theoretical approaches that are able to provide a detailed description of the M-L bond. In this work, we present a study of LMo(CO)5 complexes with L being various tertiary phosphines ligands by means of mass-selected high-resolution photoelectron spectroscopy (PES) performed with synchrotron radiation, DFT and energy decomposition analyses (EDA) combined with the natural orbitals for chemical valence (NOCV) analysis. These methods enable a separated access of the σ-donor and π-acceptor effects of ligands by probing either the electronic configuration of the complex (PES) or the interaction of the ligand with the metal (EDA). Three series of PX3 ligands with various electronic influence are investigated: the strong donating alkyl substituents (PMe3, PEt3 and PiPr3), the intermediate PPhxMe(3-x) (x = 0-3) set and the PPhxPyrl(3-x) set (x = 0-3 with Pyrl being the strong electron withdrawing pyrrolyl group C4H4N). For each complex, their adiabatic and vertical ionization energies (IEs) could be determined with a 0.03 eV precision. Experiment and theory show an excellent agreement, either for the IEs determination or for the electronic effect analysis. The ability to interpret the spectra is shown to depend on the character of the ligand. “Innocent” ligands provide the spectra the most straightforward to analyze whereas the “non-innocent” ligands (which are ionized prior to the metal center) render the analysis more difficult due to an increased number of molecular orbitals in the energy range considered. A very good linear correlation is finally found between the measured adiabatic ionization energies and the interaction energy term obtained by EDA for each of these two types of ligands which opens interesting perspective for the prediction of ligand characters

Mechanistic aspects of the stereospecific reduction of chiral hydroxyalkyl phosphinates and phosphine oxides

International audienc

Enantioselective alkylidenecyclopropanation of norbornenes with terminal alkynes catalyzed by palladium–phosphinous acid complexes

Pd(II)-coordinated phosphinous acids catalyzed the formal enantioselective [2+1] cycloaddition of norbornene derivatives with terminal alkynes. The absolute configuration of (+)-3aa was assigned using VCD

Le rat âgé reste sensible aux altérations métaboliques induites par un régime riche en sucre mais il est mal protégé par une supplémentation en micronutriments

National audienc